Propeller



Feb, 11, 1941. l C, C DUBBS 2,231,464

PROPELLER Original Filed Dec. 14, 1956 Patented Feb. 11, 1941 UNITEDSTATES PATENT OFFICE PROPELLER.A

Carbon C. Dubbs, Saginaw, Mich.

Application December 14, 1936, Serial No. 115,757 Renewed August 12,1939 1 Claim.

This invention relates to improvements in propellers, and refersspecifically to a multi-blade propeller characterized in that duringoperation connected blades perform the same amount of work irrespectiveof the medium, variations in the movement of the medium or variations ofdensity or pressure of the medium in which the blades work.

My invention, although applicable to many types of propellers forpropelling objects through a fluid medium or imparting motion oragitation to a fluid, is ideally adapted for use in conjunction withships, and although I will describe my invention in this latterenvironment, I do not wish to be limited to this specific thereof.

One of the most serious limitations to the speed and comfort of ships isthe vibration caused by the propeller when the ship is driven at highspeed. Such vibration, in a predetermined instance, may be lessenedslightly application by adding weight to the ship, but this in no wiseremedies or lessens the cause of the vibration.

Obviously,

this solution of the problem merely dodges the issue and in practice theadding of such nonpaying weight soon renders the slight benets accruingtherefrom uneconomical.

function of the following items:

1. The revolution per unit of time peller;

of the pro- 2. The speed of the water impinging upon the blade;

3. The area of the blade surfaces; and 4. The pitch of the blades withrespect to the driving axis.

Item No. 3 is constant and heretofore item No. 4 was often considered aconstant. However, propellers have been built where item No. 4 could bevaried from time to time through a manually operated screw devicerunning through a hollow shaft to the propeller whereby the pitch of allblades could be increased or decreased at the same time.

However, the pitch of the blades has heretofore been increased ordecreased equally to change boat speed while maintaining propeller R. P.M, constant.

In the above list item No. 2 is a variable.

One

of the most important functions of this variable is recognized as theeffect produced by the motion of the ship through the water.

As is well (Cl. 17m-162) known, the propeller is mounted at the rear ofthe ship normally below the Water line. When the hull of a ship movesthrough the water friction causes the water adjacent the hull surface tomove forwardly at a predetermined rate. The movement of the water is amaximum adjacent 5 the hull surface and decreases along a line normalto, and away from said surface. Further, the rate of movement of thewater is also dependent upon the length of the hull with which the waterhas contacted, resulting in a greater velocity of water adjacent thewater surface where the ships wetted length is greatest than water closeto the ship down near the keel where the ships wetted length is least.

This fact results in a variable movement of the water at the rear of theship, the medium in which the propeller operates, the movement of thewater with respect to the propeller increasing substantially inverselyas the wetted length of the ship and generally inversely as the depth.Heretofore, therefore, with items Nos. 1, 3 and 4 maintained constant,the propeller assumed a state of dynamic unbalance which, of course,resulted in vibration.

Accordingly, I have so constructed my propeller that variations in itemNo. 2 are compensated by corrective variations in item No. 4, that is,variations in the movement of the medium in which the propeller operatesautomatically causes variations in the pitch of the blades of thepropeller with respect to the driving axis.

Other objects and advantages of my invention will be apparent from theaccompanying drawing and following detailed description.

In the drawing, Fig. l is a top plan view of my propeller.

Fig. 2 is a rear elevational view of the propeller blades and asectional view taken on line 2-2 of Fig. l.

Fig. 3 is a side elevational view of the propeller as illustrated inFig. 1.

Fig. 4 is a sectional view of a blade of the propeller taken on line 4-4of Fig. 2.

Referring in detail to the drawing, I indicates a propeller shaft of aship (not shown), the shaft I projecting from the lower rear portionthereof. A longitudinally separable collar 2 is mounted upon the end ofshaft I and is secured rigidly therewith by means of pin or screw 3which is 50 countersunk below the surface of the collar. The collar 2 isof typical stream line construction so as to encounter a minimumresistance in movement through the water. For purposes of my in-Avention the collar 2 may be mounted upon shaft 55 I in any conventionalmanner, the showing of pin or screw 3 being merely for purposes of i1-lustration.

Each of the separable portions of collar 2 is provided intermediate itslength with a semicylindrical bearing surface, which when the collar isassembled, register with each other to form a bearing. The collar 2adjacent said bearing is provided with bores 5 for the reception ofscrews 6 or other fastening means, said screws being countersunk similarto screw 3. By the provision of screw 3 and screws 6, the collar 2 issecurely maintained in assembled relation.

A propeller 'l is adapted to be carried by collar 2 and comprisesappropriately pitched helicoidal blades 8 and 9 formed integral with o`rrigidly connected by shaft I0. Shaft I0 is adapted to be journalled inthe bearing provided-in collar 2 and is rotatable therein. The axisl oflrotation of shaft Il] will, for convenience, be hereinafter designatedthe compensating axis to distinguish from` the axis about which shaft lturns which will be hereinafter termed the driving axis. It can readilybe seen that the blades being rigidly connected to each other by shaftIt, maintain a fixed pitch relationship fto each other irrespective ofrotation of propeller l about the driving axis or the compensating axis,but the angular relationship of the surfaces of blades 8 and 9, that is,th'e pitch of said individual blades change with respect to the drivingaxis when shaft lil rotates.

The surfaces of blades 8 and 9 are not symmetrical about thecompensating axis, that is, the area of blade 3 upon one side of theaxis is greater than the area of the blade 8 upon the opposite side ofsaid axis, and the area of blade Son one `side of its axis is greaterthan the area of blade Qonthe opposite side of said axis. Referring toFigs. 2 vand 3, it will be seen that theyarea of the blade 8 above thecompensating axis is less than the area of said blade below said axisand with respect to blade 9 the opposite is true. Referring to thedirectionl of rotation of the propeller "l, as indicated bythe arrow,they area of each of the lblades von the leading side of thecompensating axis is less than the area on the trailing side .'thereof.Similar to the concept of the center of gravity of a body, that is, theweight of a body may be 4considered as beingk concentrated at its centerof gravity with respect to 'forces acting on vsaid bo-dy, the forceexerted by a propeller may =be considered'as originating at what maybetermed the centers ofeffort of the blades. The center of effort lofablade is primarily determinedby its effective working area and in myconstruction, the blades being of helicoidal surface, the center of`effort falls on the trailing ySicle of the compensating axis, that is,the side' of greater area. For purposes of illustration, I havedesignated said points as ll and l2 on blades 8 and 9 respectively.

Assuming propeller 1 as rotating about its driving-axis in still water,the force of reaction of the water in -the case of Vboth blades will acton a moment arm equal to the distance of each center of effort Il and l2from the compensating axis. These moment arms are equal, by constructionof the propeller, and inasmuch as still water is considered, the forcesacting will be substantially equal. Therefore, no rotation of shaft lilabout the compensating axis will take place. This condition, of course,is ideal, and in the case of ships, is never met with in practice.

Practically, as has been hereinbefore described, the movement of themedium changes the force of the water reacting at the centers of effortand one moment of force of one blade Will temporarily overbalance themoment of force of the other blade. The propeller will then rotate aboutits compensating axis, thereby changing `the pitch of the blades withrespect to the driving-axis. An equilibrium, of course, will soon beestablished when the moments of said forces will equalize each other.This, therefore, results in an arrangement wherein the moments of there- `acting forces are equalized by a change of pitch of the blades withrespect to the driving axis,

and hence each blade performs equal work irrespectiveV .of the motionalor other Yphysical 1 variations of the medium in which the blades act.

Of course, since the propeller 1 rotates about the driving axis, it isstatically balanced with respect to such axis.- However, the propelleralso rotates about the compensating axis and therefore I also staticallybalance said propeller about this axis. By-referring to Fig. 4, a crosssectional-view of one of the blades shows that the center of inertia 2does `not coincide with the center of width 3' of the blade but due toincreased thickness on the side of the leading edge 4. of the blade, thecenter of inertia falls closer to the leading edge than the trailingedge 5. In other words, th'e locus 6 of the centers of inertia of all ofthe sectional increments coincides with the compensating axis.

I claim as my invention:

A marine propeller device of the class ydescribed which comprises atwo-part collar mountedupon a rotating drive shaft, the said collar'being'split1in a plane through the axis of saidshaft and being formedintermediate its length with coacting 'semi-cylindrical portionsradially extending blades carried by said collar, said blades 'havinghelicoidal surfaces, means integral with said blades comprising acentral cylindrical element rigidly connecting said blades together tomaintain the pitch'of said blades constant with respect, to each Yotherland to maintain the compensating-axis'of the blades at right angles tothe axis of the drive shaft, said means being journaled in said coactingsemicylindrical portions and freely rotatable to change the pitch ofsaid blades with respect to the axis'of the drive shaft, the face ofeach blade von one side of the projected axis'of said compensating axisbeing greater in area than the .area of the face-of said blade'on theopposite side -of said projected axis, the center of i effort of eachblade @being von ropposite :sides of said projected 4axis-the thicknessof each blade on opposite sides -of said projected'axis-bearinganinverse'ratio to the area of said bladessto substantially staticallybalance said blade about the projected axis. -l

, CARBON C. DUBBS.

